Drum for mixing concrete and the like



Feb. 25, 1969 s. MAXON, JR 3,429,561

DRUM FOR MIXING CONCRETE AND THE LIKE Filed Nov. 17, 1967 Sheet of 4 MM 51m wayMaxan. Jr. 5

a ing Feb. 25, 1969 G. MAXON. JR

DRUM FOR MIXING CONCRETE AND THE LIKE z of 4 Sheet .Filed NOV. 17. 1967 HazzwqyMExom Yz Feb. 25, 1969 G. MAXON. JR 3,429,561 I DRUM FOR MIXING CQNCRETE AND THE LIKE Filed Nov. 17, 1967 Sheet 5 of 4 ki 5 Z4 I Feb. 25, 1969 v s. MAXON, JR

DRUM FOR MIXING CONCRETE AND THE LIKE Sheet Filed NOV- 17, 1967 United States Patent 7 Claims ABSTRACT OF THE DISCLOSURE The drum has an unusually long cylindrical medial portion, but rapid and thorough mixing is effected by scooplike rear lifting elements, near the rear of the medial portion, and front lifting elements, in the frustoconical discharging portion, which cooperate with elongated blades that extend lengthwise substantially from end to end of the drum and are skewed in the direction to urge contents forwardly as the drum rotates. Each lifting element is mounted circumferentially intermediate a pair of blades and is shaped to pick up material as it moves through the bottom of its orbit, then spoutingly discharge such material over its circumferentially trailing blade and obliquely rearwardly.

This invention relates to drum type mixers for concrete and similar plastic materials, and more particularly the invention pertains to large capacity tilting mixing drums for concrete batching plants and the like.

Typically the mixing drum of a concrete batching plant has a generally cylindrical medial portion with a concentric frustoconical charging portion at its rear and a concentric frustoconical discharging portion at its front. In use the drum is loaded with cement, aggregate and Water through a concentric hole in its charging portion and is rotated in one direction so that blades in its interior can agitate and mix the charge. When the contents of the drum are thoroughly mixed, the drum is tilted forwardly to discharge the mixed concrete out of a concentric discharging hole in its front.

-In the interior of the drum are blades that are lengthwise skewed relative to radial planes that lie on the drum axis. These agitate the drum contents during mixing and propel the contents forwardly during discharging, inasmuch as the drum is rotated during discharging in the same direction that it turns during mixing.

Heretofore it has been considered necessary for the cylindrical medial portion of a tilting mixing drum to be relatively very short in relation to its diameter, and therefore large drum capacity has been obtained by making the drum with a large diameter. The reason for this was that certain components of the material to be mixed tended to remain at the rear of the drum while others were driven toward the front of the drum by the skewed lades; and because of this tendency to axial segregation complete and thorough mixing could not be achieved during the course of any reasonably short mixing cycle in a drum having a long cylindrical medial portion.

The supposed need for a drum that had a large diameter relative to the length of its cylindrical portion was in conflict 'With the need for compactness in portable concrete mixing and batching plants. Desirably such a plant should comprise one or two trailer mounted elements that can be towed along the highways when being moved from site to site and can be erected and taken down with a minimum of time and labor. For utmost operating efliciency, and to keep erection and disassembly time to a minimum, the mixing drum of such a plant should have its axis parallel to the direction of travel of the vehicle on which it is mounted, as in the portable 3,429,561 Patented Feb. 25, 1969 batching plant of Patent No. 3,241,821 to G. Maxon, Jr. For on-highway travel, however, the diameter of the mixing drum is limited by the laws relating to vehicle width. If the cylindrical portion of the drum must be short in relation to its diameter in order to achieve a satisfactorily brief mixing cycle, the restriction of drum diameter imposes a severe limitation upon drum capacity.

The present invention has for its general object the provision of a mixing drum of the character described which can have a cylindrical medial portion that is relatively long, so that the drum has a high capacity for its diameter, but which nevertheless achieves very rapid and thorough mixing.

Thus it is another and more specific o ject of this invention to provide agitator means for a tilting mixing drum of the character described whereby a rolling or interfolding motion, both axially and circumferentially, is imparted to the contents of the drum to effect very rapid and thorough mixing thereof.

Of course the rapidity with which mixed material can be discharged from a mixing drum is one of the factors that determine the time required for a complete mixing cycle; and therefore the discharging opening of a small diameter high capacity drum should have an effective diameter which is not substantially smaller than that of a heretofore conventional large diameter drum of the same capacity. However, the effective diameter of the concentric discharging hole in the front of the drum has a bearing upon drum capacity, for if it is large relative to the drum diameter, the capacity of the drum is correspondingly limited. This is immediately apparent from the obvious fact that the drum cannot be filled to a level above the bottom of its openings. Actually, the drum cannot even be filled to that level because of the tendency of its lengthwise skewed blades to propel the water and fines forwardly out of the discharge hole as the drum rotates during mixing.

With the last mentioned consideration in mind, it is another object of this invention to provide a tilting mixing drum of the character described which has a large capacity relative to its diameter, in that it can be filled to a relatively high level without danger that its contents will -be sloshed out of the discharging hole during mixing, but which is nevertheless capable of discharging its contents very rapidly.

More specifically, it is another object of this invention to provide means by which the diameter of the discharging opening in a mixing drum of the character described is maintained effectively small while the drum is mixing, to thereby enable the drum to have a large capacity, but which means is readily distensible by material issuing out of said opening during discharging of the drum contents so that such discharging can take place very rapidly.

With these observations and objects in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings. This disclosure is intended merely to exemplify the invention. The invention is not limited to the particular structure disclosed, and changes can be made therein which lie within the scope of the appended claims without departing from the invention.

The drawings illustrate several complete examples of the physical embodiment of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIGURE 1 is a fragmentary view in side elevation of a portion of a concrete mixing plant incorporating a mixing drum that embodies the principles of this invention;

FIGURE 2 is a view in side elevation, on a larger scale, of the mixing drum per se of this invention;

FIGURE 3 is a perspective view of the mixing drum of this invention as it would appear with its discharging portion removed, looking into it toward the charging opening at its rear;

FIGURE 4 is a fragmentary perspective view of the drum of this invention with its discharging portion re moved and with parts of its medial and charging portions broken away, looking obliquely rearwardly into the drum;

FIGURE 5 is a perspective view of the interior of the discharging portion of the drum of this invention, looking obliquely forwardly; and

FIGURE 6 is a fragmentary view of the front end portion of the drum, partly in side elevation and partly in longitudinal section.

Referring now to the accompanying drawings, the numeral 5 designates generally a frame that comprises part of a concrete mixing or batching plant and upon which a drum 6 of this invention is mounted for rotation about its axis and for bodily tilting motion between a normal position (shown in FIGURE 1) in which the drum axis is substantially horizontal and a discharging position (indicated in broken lines in FIGURE 2) in which the drum axis is substantially inclined to the horizontal. The frame 5 comprises upright legs 7 which are suitably braced and a yoke 8 upon which the drum is carried for rotation. The yoke is actuated for drum tilting motion by means of double-acting hydraulic cylinders 9 that are connected between it and fixed parts of the frame. Rotation is imparted to the drum through a ring gear 10 on its medial portion.

The means by which the drum is mounted on the yoke for rotation and by which it is rotatably driven are well known and are therefore not illustrated. As is conventional with tilting mixing drums, the drum 6 is intended to be rotated during discharging in the same direction that it rotates during mixing, in order to expedite discharge of its contents.

In general the mixing drum of this invention has a cylindrical medial portion 11, a concentric, axially short, frustoconical charging portion 12 on the rear of its medial portion, and a concentric frustoconical discharging portion 13 on the front of its medial portion, the discharging portion 13 having a substantially greater axial length than the charging portion.

The charging portion has a substantially flat end wall 14 in which there is a concentric charging opening 15, while the discharging portion tapers all the way to a concentric discharging opening 16 that is preferably somewhat smaller than the charging opening.

Those familiar with tilting concrete mixers will no doubt be impressed with the unusual length of the cylindrical medial portion 11 of the drum of this invention, which is almost twice as long in proportion to its diameter as the corresponding portion of prior tilting mixing drums. This long medial portion of the drum is made possible by the agitating means in the drum, now to be described, and accounts for the high capacity of the drum of this invention relative to its diameter.

In general the agitating means in the drum of this invention comprises a plurality of elongated blades 18, and a plurality of scoop-like lifting elements or buckets that are located in axially spaced zones in the drum, with the lifting elements in each zone mounted circumferentially intermediate the blades. As shown, there are four circumferentially equispaced blades 18 in the drum, and there are four rear lifting elements or buckets 19 in the medial portion of the drum, and four front lifting elements 20 in the discharging portion of the drum, each of the front and rear lifting elements being mounted circumferentially intermediate two adjacent blades.

The blades 18 extend lengthwise in the drum from near the end wall 14 of its charging portion to near the discharging opening 16. Each blade thus comprises three sections, namely a rear section 21 in the charging portion of the drum, a medial section 22 in the medial portion of the drum, and a front section 23 in the discharging portion of the drum.

Each blade section is mounted on a pair of substantially triangular brackets 24 that are welded to the blade section and to the inner drum surface. The brackets support the blade section with its outer longitudinal edge 25 adjacent to the inner surface of the drum but spaced slightly therefrom, and with its inner longitudinal edge 26 substantially nearer the drum axis than its outer longitudinal edge. Preferably each blade section is bowed or otherwise bent across its width to have a concave surface that faces generally in the direction of drum rotation.

Each of the rear blade sections 21 is lengthwise skewed so that its outer longitudinal edge 25 extends obliquely to a radial plane that lies on the drum axis, such skew being in the direction to cause the blade to urge material forwardly in the drum as it rotates. Each of the medial blade sections 22 is similarly skewed, but to a greater extent. Each of the front blade sections 23 has its outer edge 25 substantially on a radial plane that lies on the drum axis; but because of the frustoconical shape of the discharging portion 13 of the drum the front blade sections tend to assist the drum contents in moving toward the discharge opening when the drum is tilted. However, the front blade sections are negatively raked to some extent, that is, the inner longitudinal edge 26 of each front blade section trails its outer longitudinal edge 25 during drum rotation; and because of this negative rake and the frustoconical shape of the discharging portion 13, by which the longitudinal edges of each front blade section are disposed obliquely to the drum axis, the front blade sections tend to move the contents of the drum toward the rear thereof as the drum rotates in its mixing position. The rear and medial blade sections preferably have a lesser amount of negative rake than the front blade sections.

As each blade moves through the bottom of its orbit it tends to plow its way through the material in the drum without effecting any substantial mixing of it; but as it moves upwardly in its orbit it carries a portion of the material along with it, since the blade and the Wall of the drum cooperate to define a chutelike trough. Because of the skew of the blade, the material thus carried upwardly by the blade is gravity urged lengthwise forwardly down the incline of the blade as well as being spilled over the blades inner longitudinal edge 26. Thus the blades themselves have an action generally similar to that of the blades in prior mixing drums.

In the mixer of this invention, however, the scooplike lifting elements 19 and 20 serve to prevent axial segregation of the materials in the drum and greatly improve and expedite the mixing action. Specifically, each lifting element or bucket picks up material as it moves through the bottom of its orbit and then spoutingly discharges such material axially rearwardly and radially inwardly over the inner longitudinal edge of the blade that trails it. Thus the lifting elements, in throwing material toward the rear of the drum, counteract the tendency of the blades to keep it at the front of the drum, and at the same time the lifting elements cooperate with the blades to produce a complex rolling and interfolding agitation of the drum contents that is very effective in achieving rapid and thorough mixing.

The rear lifting elements 19 are generally scoopshaped and are mounted near the rear end of the cylindrical medial portion 11 of the drum, each being carried On a pair of triangular brackets 29 that are welded to the drum and to the lifting element. Each of the rear lifting elements has an outer edge 31 that is adjacent to the inner surface of the drum but is preferable slightly spaced therefrom, and has an inner edge 32 that is substantially closer to the drum axis than the inner edges 26 of its adjacent blade sections. Each rear lifting element is bent or bowed to have a surface which is concave across its width, from one side edge 33 to the other, and

which faces generally in the direction of drum rotation. Further contributing to its scoop-like shape, its inner edge 32 can be rounded and its side edges 33 can be somewhat convergent toward its inner edge.

The rear lifting elements have little or no rake but have a small amount of skew so that their concave surfaces face slightly toward the rear of the drum as well as generally in the direction of drum rotation. Thus each rear lifting element spoutingly discharges circumferentially over the edge of its trailing blade and obliquely toward the rear of the drum. To insure that the material discharging from each rear lifting element will clear its trailing blade, the inner edge of each medial blade section 22 can be cut down somewhat, as at 35, near the rear end thereof, and the rear blade sections 21 can be substantially narrower than the main part of the medial blade sections.

Each of the front lifting elements 20 can be substantially trapezoidal in shape, with an outer edge 37 that is adjacent to but slightly spaced from the inner surface of the discharging portion, a straight inner edge 38, and straight, slightly convergent side edges 39. Each front lifting element is curved or bent to have a surface which is concave across its width, from side edge to side edge, and which faces generally in the direction of drum rotation. Each is mounted on a pair of triangular brackets 40 that are welded to the inner surface of the discharging portion and to the lifting element, and each is disposed with its rear side edge near the front edge of the medial portion 11 of the drum. The front lifting elements can have a small amount of negative rake and can be skewed somewhat so that their concave surfaces face obliquely slightly toward the rear of the drum. Thus each of the front lifting elements discharges into the rearmost part of the frustoconical discharging portion of the drum, and to a greater extent, into the front of the cylindrical medial portion; and such discharge from each front lifting element of course takes place in a manner to spout the discharged material over the inner edge 26 of its trailing blade.

Cooperating with the elongated cylindrical medial portion of the drum to increase its capacity is a coaxial projection 42 on the front of the frusto-conical discharge portion that is somewhat like an iris diaphragm and serves, during mixing, to reduce the effective diameter of the discharge opening and to effectively establish the outlet from the drum at a location that is a distance forwardly of the discharge opening 16, thereby greatly reducing the chances for material to be propelled out of the drum by the agitating means as mixing proceeds.

As illustrated in FIGURES l, 2 and 6, the projection 42 comprises a plurality of forwardly and inwardly projecting rectangular blades 43 of rubber-like material that are arranged with their edge portions overlapping. The blades 43 have their rear end portions secured to frustoconical ring segments 44 that overlie the front end portion of the discharging portion 13 of the drum, several blades being secured to each ring segment and the several ring segments being secured to the drum shell in circumferentially adjacent relation to one another to encircle its front end. An outer frusto-conical ring 45 overlies the rear end portions of the blades to cooperate with the ring segments 44 in holding them in place.

Normally, during mixing, the blades are unfiexed and cooperate to define a fairly small opening 46 at the front of the forward extension 42, so that water and fines are prevented from being sloshed out of the drum. If the mixture in the drum is a relatively wet one, such as is intended to be discharged into a truck mixer, the blades flex little or not at all when the drum is tilted to discharge its contents, and the relatively small opening defined by the blades facilitates discharge directly into the narrow opening of a truck mixer. However the weight of a heavy, viscous mix passing over the blades during discharge of the drum contents tends to fiex them radially outwardly as shown in FIGURE 6, with the result that the opening which the blades define is substantially enlarged to expedite discharge of the drum contents. When the drum is tilted, however, heavy material issuing from it can flex the blades radially outwardly, thereby distending the outlet which they define so that the projection 42 presents no substantial obstruction to discharge of material from the discharging hole 16.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides a tilting mixing drum for concrete and the like that has a very high capacity in proportion to its diameter, and that the mixing drum of this invention is nevertheless capable of effecting very rapid and thorough mixing and quick discharge of its contents.

What is claimed as my invention is:

1. In a mixing drum for concrete and the like of the type that is mounted for rotation on its axis and has a substantially cylindrical medial portion, an inwardly convergent wall on the rear end of said medial portion in which there is a concentric charging opening, and a coaxial frusto-conical discharging portion on the front end of said medial portion in which there is a concentric discharging opening:

(A) a plurality of elongated blades mounted in the interior of the drum at circumferentially spaced intervals, each extending lengthwise from near the charging opening to near the discharging opening and having an outer longitudinal edge adjacent to the inner surface of the drum and an inner lonitudinal edge which is nearer the drum axis than said outer longitudinal edge, each of said blades being generally lengthwise skewed relative to a plane radial to the drum axis in the direction to urge material forwardly in the drum as it rotates; and

(B) a plurality of scoop-like lifting elements mounted in the interior of the drum forwardly of its charging portion, each circumferentially intermediate a pair of blades, each having an outer edge adjacent to the inner surface of the drum and an inner edge substantially nearer the drum axis than the inner edges of its adjacent blades, and each having a surface that is concave from side edge to side edge and faces obliquely in the direction of drum rotation and axially forwardly in the drum so that the lifting element is adapted to carry material upwardly as it moves away from the bottom of its orbit and to spoutingly discharge such material axially towards the rear of the drum and over its trailing blade.

2. The mixing drum of claim 1 further characterized yieldingly resilient means on the discharging portion of the drum normally defining a substantially frustoconical forward extension of the drum having an opening in its front end which is substantially smaller than said discharging hole, said means being radially distensible by heavy material flowing therethrough from the discharging hole so as to present little restriction to flow of such material.

3. The mixing drum of claim 2, further characterized said yieldingly resilient means comprising a plurality of elongated resilient blades secured to the discharging portion of the drum and projecting obliquely forwardly and radially inwardly therefrom.

4. The mixing drum of claim 1, further characterized (A) one of said lifting elements being mounted between each pair of blades in the medial portion of the drum; and

(B) one of said lifting elements being mounted between each pair of blades in the discharging portion of the drum.

5. The mixing drum of claim 4, further characterized said lifting elements in the medial portion of the drum being mounted near the rear end thereof.

6. In a mixing drum for concrete and the like of the type that is mounted for rotation with its axis substantially horizontal during mixing and which has a coaxial discharging opening at one end thereof:

(A) a plurality of blades mounted on the wall of the drum, at the interior thereof and at circumferentially spaced intervals around the drum, said blades being elongated in the general direction of the drum axis but being lengthwise skewed so that material lifted by the blades from the bottom of the drum as they move upwardly in their orbits is spilled radially inwardly while being moved axially toward the discharging opening; and

(B) a plurality of scoop-like lifting elements associated with each blade and spaced apart lengthwise thereof, each supported in the drum from the wall thereof intermediate circumferentially adjacent blades and ahead of its associated blade in the direction of drum rotation, each of said lifting elements being 8 arranged to pick up material as it moves through the bottom of its orbit and, as it moves upwardly in its orbit, to spoutingly discharge such material obliquely radially inwardly past its associated blade and away from the discharge opening. 7. The mixing drum of claim 6, further characterized by:

each of said lifting elements projecting farther into the drum radially than the adjacent portion of its associated blade.

References Cited UNITED STATES PATENTS 1,220,683 3/1917 Ransome 259175 2,611,591 9/1952 Longenecker 259--175 2,614,819 10/1952 Longenecker 259-175 2,708,570 5/1955 Manabe 259175 3,241,821 3/1966 Maxon 259175X 20 ROBERT W. JENKINS, Primary Examiner. 

